A variety of industrial applications exist where power ultrasonic actuators are used to produce large amplitude vibrations. These applications include medical/surgical, automotive, food preparation space applications and textile cutting applications, as well as use in fabrication industries and material joining. Ultrasonic actuators are attractive for their ability to generate precision high strokes, torques and forces while operating under relatively harsh conditions, such as temperatures in the range of single digit Kelvin to 1273 Kelvin.
NASA in-situ exploration missions, such as the Phoenix and MSL missions, are increasingly requiring analysis of acquired samples to detect and characterize the presence of potential biomarkers of life and water, as well as determine the geological properties. For these missions, there is a need to produce samples using effective mechanisms. Samplers based on the ultrasonic/sonic percussive mechanism, also known as ultrasconic driller/corers (USDCs), have shown promise in support of such missions. In part the USDC has utility for space applications because it requires low axial preload on the bit, allowing drilling from low-mass platforms.
The free-mass is an element in the activation of the ultrasonic/sonic percussive mechanism. It performs frequency reduction from the ultrasonic (or high frequency) vibration produced by the piezoelectric actuators to the sonic (or low frequency) vibration required for effective drilling. In some USDC designs, the frequency is reduced from about 20 kHz to about 60-1,000 Hz. The free-mass is placed in between the horn and the bit and is free to move axially between the horn and the bit. FIG. 1 shows a prior art design of a free-mass which has a cylindrical geometry with a center hole. This design has at least the problem that the free-mass tends to jam. This results in the termination of operation of the USDC. In addition once jammed, the system is difficult to disassemble.
There is a need for an USDC that address the operational limitations of the prior art, including the tendency of these systems to jam, so as to improve the performance and operational reliability of drillers and corers that are driven by a ultrasonic/sonic percussive mechanism.